Project description:The ground state of pluripotency is defined as a basal proliferative state free of epigenetic restriction, represented by mouse embryonic stem cells (ESCs) cultured with two kinase inhibitors (so-called “2i”). Through comparison with serum-grown ESCs, we identify epigenetic features characterizing 2i ESCs by proteome profiling of chromatin including post-translational histone modifications. The most prominent difference is H3K27me3 and its enzymatic writer complex PRC2 that are highly abundant on eu- and heterochromatin in 2i ESCs, with H3K27me3 redistributing outside canonical PRC2 targets in a CpG-dependent fashion. Using PRC2-deficient 2i ESCs, we identify epigenetic crosstalk with H3K27me3, including significant increases in H4 acetylation and DNA methylation. This suggests that the unique H3K27me3 configuration protects 2i ESCs from preparation to lineage priming. Interestingly, removal of DNA methylation in PRC2-deficient 2i ESCs lacking H3K27me3 using 5-azacytidine hardly affected ESC viability and transcriptome, showing that ESCs are independent of both major repressive epigenetic marks.
Project description:Embryonic stem cells (ESCs) of mice and humans have distinct molecular and biological characteristics, raising the question whether an earlier ‘naive’ state of pluripotency may exist in humans. Here we took a systematic approach to identify small molecules that support autonomous self-renewal of naive human ESCs based on maintenance of endogenous OCT4 distal enhancer activity, a molecular signature of ground state pluripotency. Iterative chemical screening identified a combination of five kinase inhibitors that induces and maintains OCT4 distal enhancer activity when applied directly to conventional human ESCs. These inhibitors generate a homogeneous population of human pluripotent stem cells in which transcription factors associated with the ground state of pluripotency are highly upregulated. Comparison with previously reported naive human ESCs indicates that our kinase inhibitor cocktail captures a novel pluripotent state in humans that closely resembles mouse ESCs. ChIP-seq data from human embryonic stem cells in naive and primed conditions were generated by deep sequencing using Illumina Hi-Seq 2000.
Project description:Human and mouse embryonic stem cells (ESCs) are derived from blastocyst stage embryos but have very different biological properties, and molecular analyses suggest that the pluripotent state of human ESCs isolated so far corresponds to that of mouse derived epiblast stem cells (EpiSCs). Here we rewire the identity of conventional human ESCs into a more immature state that extensively shares defining features with pluripotent mouse ESCs. This was achieved by exogenous induction of Oct4, Klf4 and Klf2 factors combined with LIF and inhibitors of glycogen synthase kinase 3 (GSK3) and mitogen-activated protein kinase (ERK) pathway. Forskolin, a protein kinase A pathway agonist that induces Klf4 and Klf2 expression, can transiently substitute for the requirement for ectopib transgene expression. In contrast to conventional human ESCs, these epigenetically converted cells have growth properties, an X chromosome activation state (XaXa), a gene expression profile, and signaling pathway dependence that are highly similar to that of mouse ESCs. Finally, the same growth conditions allow the derivation of human induced pluripotent stem (iPS) cells with similar properties as mouse iPS cells. The generation of “naïve” human ESCs will allow the molecular dissection of a previously undefined pluripotent state in humans, and may open up new opportunities for patient-specific, disease-relevant research.
Project description:<p>In this study we used next generation deep sequencing technologies to analyze the genomes of Harvard University Stem Cell lines 63 and 64. We performed 101-bp paired-end whole genome sequencing of the two cell lines using Illumina HiSeq platforms. The sequence reads obtained were analyzed for copy number and used for replication timing analysis. Our data suggests that read depth profiles can be used to map replication timing in Embryonic Stem Cells (ESCs). Further we observe that replication profiles are highly correlated across ESCs but distinct from those of other cell types such as Lymphoblastoid Cell Lines (LCLs). These results demonstrated that read depth data from whole genome sequencing can be used to study variation in replication timing within the human population and across different cell types. Whole genome sequences from HUES63 and HUES64 used for this study are being submitted.</p>
Project description:Embryonic stem cells (ESCs) of mice and humans have distinct molecular and biological characteristics, raising the question whether an earlier ‘naive’ state of pluripotency may exist in humans. Here we took a systematic approach to identify small molecules that support autonomous self-renewal of naive human ESCs based on maintenance of endogenous OCT4 distal enhancer activity, a molecular signature of ground state pluripotency. Iterative chemical screening identified a combination of five kinase inhibitors that induces and maintains OCT4 distal enhancer activity when applied directly to conventional human ESCs. These inhibitors generate a homogeneous population of human pluripotent stem cells in which transcription factors associated with the ground state of pluripotency are highly upregulated. Comparison with previously reported naive human ESCs indicates that our kinase inhibitor cocktail captures a novel pluripotent state in humans that closely resembles mouse ESCs.
Project description:Embryonic stem cells (ESCs) of mice and humans have distinct molecular and biological characteristics, raising the question whether an earlier ‘naive’ state of pluripotency may exist in humans. Here we took a systematic approach to identify small molecules that support autonomous self-renewal of naive human ESCs based on maintenance of endogenous OCT4 distal enhancer activity, a molecular signature of ground state pluripotency. Iterative chemical screening identified a combination of five kinase inhibitors that induces and maintains OCT4 distal enhancer activity when applied directly to conventional human ESCs. These inhibitors generate a homogeneous population of human pluripotent stem cells in which transcription factors associated with the ground state of pluripotency are highly upregulated. Comparison with previously reported naive human ESCs indicates that our kinase inhibitor cocktail captures a novel pluripotent state in humans that closely resembles mouse ESCs.
Project description:Human pluripotent stem cells can be derived from somatic cells by forced expression of defined factors, and more recently by nuclear-transfer into human oocytes, revitalizing a debate on whether one reprogramming approach might be advantageous over the other. Here we compared the genetic and epigenetic stability of human nuclear-transfer embryonic stem cell (NT-ESC) lines and isogenic induced pluripotent stem cell (iPSC) lines, derived from the same somatic cell cultures of fetal, neonatal and adult origin. Both cell types shared similar genome-wide gene expression and DNA methylation profiles. Importantly, NT-ESCs and iPSCs have comparable numbers of de novo coding mutations but significantly higher than parthenogenetic ESCs. Similar to iPSCs NT-ESCs displayed clone- and gene-specific aberrations in DNA methylation and allele-specific expression of imprinted genes, similarly to iPSCs. The occurrence of these genetic and epigenetic defects in both NT-ESCs and iPSCs suggests that they are inherent to reprogramming, regardless of the underlying technique. RNA sequencing analysis was performed on a total of 12 human cell lines, including: an isogenic set of 3 nuclear-transfer embryonic stem cell (NT-ESC) lines, 2 RNA-reprogrammed induced pluripotent stem cell (iPSC) lines and their parental neonatal fibroblast cell line; an isogenic set of 1 NT-ESC line, 3 iPSC lines and their parental adult fibroblast cell line (derived from a type 1 diabetic subject); as well as 1 control embryonic stem cell (ESC) line.
Project description:Human pluripotent stem cells can be derived from somatic cells by forced expression of defined factors, and more recently by nuclear-transfer into human oocytes, revitalizing a debate on whether one reprogramming approach might be advantageous over the other. Here we compared the genetic and epigenetic stability of human nuclear-transfer embryonic stem cell (NT-ESC) lines and isogenic induced pluripotent stem cell (iPSC) lines, derived from the same somatic cell cultures of fetal, neonatal and adult origin. Both cell types shared similar genome-wide gene expression and DNA methylation profiles. Importantly, NT-ESCs and iPSCs have comparable numbers of de novo coding mutations but significantly higher than parthenogenetic ESCs. Similar to iPSCs NT-ESCs displayed clone- and gene-specific aberrations in DNA methylation and allele-specific expression of imprinted genes, similarly to iPSCs. The occurrence of these genetic and epigenetic defects in both NT-ESCs and iPSCs suggests that they are inherent to reprogramming, regardless of the underlying technique. Genome-wide DNA methylation profiling by Illumina Infinium HumanMethylation 450K Beadchip was performed on a total of 21 human cell lines, including: an isogenic set of 3 nuclear-transfer embryonic stem cell (NT-ESC) lines, 2 RNA-reprogrammed induced pluripotent stem cell (iPSC) lines and their parental neonatal fibroblast cell line; an isogenic set of 1 NT-ESC line, 6 iPSC lines and their parental adult fibroblast cell line (derived from a type 1 diabetic subject); as well as 7 control embryonic stem cell (ESC) lines.
Project description:Understanding the molecular underpinnings of pluripotency is a prerequisite for optimal maintenance and application of embryonic stem cells (ESCs). While the protein-protein interactions of core pluripotency factors have been identified in mouse ESCs, their interactome in human ESCs (hESCs) has not to date been explored. Here we mapped the OCT4 interactomes in naïve and primed hESCs, revealing extensive connections to mammalian ATP-dependent nucleosome remodeling complexes.
Project description:In mammals, many germline genes are repressed by epigenetic mechanisms to prevent their illegitimate expression in embryonic and somatic cells. To advance our understanding of the complete mechanisms restricting the expression of germline genes in mammals, we analyzed the chromatin signature of germline genes and performed a genome-wide CRISPR-Cas9 knock-out screen for genes involved in germline gene repression using a reporter system in which GFP is under the control of the epigenetically repressed Dazl germline promoter in mouse embryonic stem cells (ESCs). We showed that the repression of germline genes mainly depends on the polycomb complex PRC1.6 and DNA methylation, which function additively in mouse ESCs. Furthermore, we identified and validated several novel genes involved in the repression of germline genes, and characterized three of them: Usp7, Shfm1 (also known as Sem1) and Erh. Inactivation of Usp7, Shfm1 or Erh led to the upregulation of germline genes, as well as retrotransposons for Shfm1, in mouse ESCs. Functionally, Usp7 acts at two levels: firstly it associates with PRC1.6 components and represses germline genes independently of DNA methylation, and secondly it facilitates DNA methylation deposition at germline genes for long term repression. In summary, our study provides a global view of the epigenetic mechanisms and novel factors required for silencing germline genes in embryonic cells.